Circuit connection of electron discharge apparatus



R. A. HEISING.

CIRCUIT CONNECTION 0F ELECTRON DISCHARGE APPARATUS.

APPLICATION FILED own. 1916.

1,432,022, Patented Oct. 17,1922.

/1 1/6/7701 Raymond A. He/s 017.

b I h Patented Oct 17,1922.

TED STATES RAYMOND A. nmsme, or EASTORANGE, new JERSEY, assronon 'rowns'mart ELECTRIC COMPANY, mconronarnn, or NEW YORK, N. 1., ACORPORATION 0F new YORK.

omcurr commoner: or ELECTRON DISCHARGE arraaarus.

To all whom it may concern:

Be it known that I, RAYMOND A. HEIsINc, a citizen of the United States,residing at East Orange, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in Circuit Connectionsof Electron Discharge Apparatus, of which the following is a full,clear, concise, and exact description.

This invention relates to circuit connections for electron dischargeapparatus and more especially to electron discharge apparatus of the.type in which a filamentary cathode enclosed in an evacuated vessel isprovided with means for heating the filament to incandescence to causeit to emit electrons, which may serve to convey a space current to acooperating anode enclosed in the same envelope. Such devices may beused for producing X-ray or rectifying alternating currents, or whenprovided with a controlling grid, as in vacuum tubes of the audion type,for amplifying variable currents, detecting wireless signals, and forvarious other purposes.

It has been customary prior to my invention to provide, for heating thecathode, a direct current source, such as a battery or direct currentgenerator. The external circuit connections to the cathode have beengenerally made to one side of the filament, and as a result all parts ofthe filament have not been of the same otential with respect to theanode or the grid, the difference between extreme ends being equal tothe voltage impressed upon the filament. Where a'source 'of directcurrent is employed, this voltage or difi'erence of potential isconstant, and therefore will not produce variations in the operation ofthe device. It is, however, more convenient in some cases to employ analternating current for heating the filament,

this being particularly true when a large number of suchtubes areoperated simultaneously, requiring a considerable amount of power forthe heating of the filament. Upon the substitution of such analternating current heating source for the filament, the variations ofpotential difference between the grid and filament or the plate andfilament which are thereby introduced,

potential of the filament with grid 13, and the other terminal connectedto Application filed October 11,1916. Serial No. 124,953.

may seriously affect the efiicient operation of the device. 5

The object of this invention is to provide an improved clrcuitconnection for electron dlscharge devices whereby alternating currentmay be employed forheating the filament, and the disadvantage abovementioned, as well as others which will hereafter appear, may beovercome.

In the practical application of my invention, current for heating thefilament is obtamed directly from an alternatingcurrent, generator orfrom the secondary of a transorme'r, and the connections from anode andgrid to the cathode are made to some point in the filament circuit whichhas a potential equal to the average potential of the filament which ineneral is that of the middle point of the filament. When the connections are made in this way, the average voltage or difierence ofpotential at any instant between different portions of the cathode andthe grid, and the anode, due to the heating current, will be zero.

The invention will be better understood by reference to the accompanyingdrawing and following specification, in which Fig. 1 represents anembodiment of this invention shown in connection with an electrondischarge device; Fig. 2 is a modification of Fig. 1; Fig. 3 shows howthis invention may be applied simultaneously to a pluralit of electrondischarge devices; and Fig. 4. i lustrates how a non-inductiveresistance may be employed to obtain the desired average respect to thegrid and cathode.

Referring to Fig. 1, there is shown a vacuum tube .10 of the audion typecontaining the usual heated filament 12, grid 13 and plate 14..Connected to the input terminals 12 and 13, is some'source of variable.currents to be amplified or rectified or otherwise operated upon. Inthis case there-is shown a microphone transmitter 16 in circuit with abattery 17 and the primary 18 of the transformer 19. The secondary 20 ofsaid transformer has. one terminal connected to the the filament 12 ina-manner hereafter described. Across the terminals of the secondi arywinding 20 is connected a resistance 21 for the purpose of makin theimpedance of the input circuit, as viewed from the primary coil 18, thesame for all impressed fre quencies. The output circuit is of anywellknown form, such as that shown, and com,-

prises a source of direct current 24 and the connection of the filamentto the external circuits, in view of the prior art would be to connectone terminal of the coil 20 and the negative pole of the battery 24 toone terminal of the filament. This, however, leads to the disadvantagesmentioned above,-that there will be continual variations in thepotential between the filament and grid, and between the filament andplate. To overcome this disadvantage, a connection is made from themiddle point of the filament 12, as shown. at 31, to a point 32comm'on.to both the input and output circuits. As a result,

the average voltage or difference of potential between differentportions of the cathode and grid and anode, due to the heating current,will be zero.

One inconvenience of the arran ement as shown in Fig. 1 is the necessityof aving an additional terminal comin through the yvall of the vacuumtube 10. his inconvenience may be overcome by arranging the circuit asshown in Fig. '2. In this circuit there is shown a similar source ofalternating currents adapted to be used as the input of a tube 35, thesaid tube bein similar in every respect to that shown in ig. 1. Theexternal circuit, comprising the input and the output circuits, is alsosimilar in every respect. In this Fig. 2, however, the point 32 of thecircuit, which is common to both the input and the output circuits, isconnected to the'middle point of the secondary 36 of the transformer 37.The primary 38of.this transformer is supplied from the alternatingcurrent generator 29, and in general it will be desirable to have someregulating device, such as39, to control the current delivered by thegenerator. In this case again the same purpose is accomplished as inFig. 1,

namely, that the external circuits are connected to such a point in thefilament circuit that the average difference of potential at any instantbetween difi'erenhportions of the cathode and grid and anode, due to theheating current, will be zero.

In this Fig. 2 there are shown two condensers 41 and 42, each connectedacross one half of the transformer secondary 36. These condensers areused for the purpose of aifording a low impedance path for thealternating currents in the input and output circuits, but they shouldbe of such dimensions as to offer a reasonably high impedance to thealternating current from the generator 29.

- Referring to Fig. 3, the invention is shown adapted to a wirelesssystem such as is described in the U. S. Patent No. 1,388,- 450 to C01itts and Arnold, issued August 23, 1921. n this figure there is shown anincoming circuit 45, which, by mleans of the transformer 46, may impresssuitable signals upon the input circuit of a bank of audion amplifiers48. In eneral, for such a system as shown here, t e incoming signalswill consist of high frequency oscillations modulated in accordance withlow fre- I quency signals. Each of the. amplifiers 48 comprises theusual filaments, plates and grids. In this figure the filaments are sown as connected in parallel, and the plates are similarly shown asconnected in parallel,and the grids are also shown as connected inparalleL- The usual direct our rent source 50 is supplied for the outputcircuit, this source consisting of stora e batteries or a direct currentgenerator. T e output circuit is finally connected in a suitable mannerto an antenna system 51, all in a manner fully described in theabovementioned a plication of Colpitts andArnold.

The fi aments are shown in this figure as beingadapted tobe heated by analternating current in accordance with thisinvention, the enerator 29and transformer 37 being of the same form as. shown in Fig. 2. In somecases, however,'it may be inconvenient or impossible to make aconnection to the middle point of the transformer secondary 36.Accordingly, there is placed across the terminals of said secondaryan-impedance or choke coil 52, and from; the middle point of thisimpedance52 a connection is made to the point 32 common to the input andoutut circuits of the amplifier system. The impedance of this coil ispreferably sufliciently high to revent the passage of much current fromt e generator 29, but should have a reasonably-small direct currentimpedance for the current from thebattery 50. As shown in the drawing,both halves of retard coil 52 are wound in the samedire'ction so thatthe retard coil acts non-inductively to signaling currents received fromline45. As described in connection with Fig. 2, there are shown twocondensers 53' and 54, each connected across-one-half of the impedance52, these condensers being supplied to offer a low impedance path forthe high frequency current to be amplified and transmitted from theantenna 51. As in Fig. 2,

. nectiofi from the point 32 to the middle of of said auto-transformer.

' that the transformer 37 of this Fig. 3 may therefore be dispensed withif the generator 29 is of a suitable volta e. Also this impedance 52may, obvious y, be used in connection with the circuits of Fig. 1 orFig. 2

either with or without the transformers shown in said circuits.

The impedance 52 may, furthermore, be

replaced by a non-inductive resistance such as shown in Fig. 4. In sucha case the circuit connections will be similar in every respect, withthe exception that the negative pole of the battery should be connectedwhich the deleterious effects arisin to one end 56 of the resistance 54.This is preferable to having the connection made to the middle of theresistance 54, in order that the space current from the filament maypass directly to the battery 55 without having to pass through the highresistance 54. In view of the fact that the current in the input circuitis exceedingly small, it will be permissible to make the contact fromthe input circuit directly with the ,middle point 57 of the resistance54. This arrangement has the disadvantage that the voltage between thefilament and the anode will fluctuate slightl in view of the variablefall of potential a ong the half of the resistance from 56 to 57. Suchdis-c advantage ma be overcome or neutralized, however, by s idin thepint of contact of the input circuit min t e point 57 to the point 58slightly to one side, and by such an amount that the fall of potentialbetween 57 and 58 multiplied by the amplifying coefii cient of theamplifier shall be equal and op-- posite to the fall of potentialbetween the points 56 and 57.

A number of circuits have now been described, in each of which analternating current is used for heating the filament or filaments of avacuum tube system, and in ,from potential variations are overcome. t isto be understood, however, that the invention is not limited to thecircuits shown, and that numerous changes may be madein the circuitswithout departing from the spirit of this invention. a

'What is claimed is:

1. The combination with an electron discharge device comprisin anevacuated envelope having therein a lamentary cathode and a cooperatinganode, of a transformer connected to a source of alternatin current andhaving its secondary connecte to said cathode for heating it toincandescence, an

It is apparent external circuit connection between said anode and thecentral point in the secondary Winding of said transformer, and acondenser connected across each half of said secondary adapted toofl'era low impedance path to input frequencies and a high impedancepath to the heating generator frequency. v 2. The combination with aplurality of electron discharge devices of the audion type eachcomprising an evacuated envelope having a filamentary cathode and adischarge controlling grid, the grids being connected in parallel andthe filaments being connected in parallel, of a transformer connected toa source'of alternating current and having its secondary connected tosaidcathodes for heating them to incandescence, and an externalconnection from said grids to the cen t-ral point in the secondarywinding of said transformer.

3. In combination a vacuum tube having an anode, a cathode and a controlelectrode, a. source of alternating current for heating said cathode,.an impedance between said source and said cathode, a connection betweensaid control electrode and the midpoint of said impedance, and acondenser across said impedance. v

4. In combination a vacuum tube having an anode, a cathode and a controlelectrode,

a source of alternating current for heating said cathode, an impedancebetween said source and said cathode, a connection from the midpoint ofsaid impedance to said control electrode. and a condenser across eachhalf of said impedance.

5. An electron discharge device having a thermionic cathode and an inputcircuit, a transformer connected to said cathode for supplying heatingcurrent thereto, a path in shunt to the secondary of said transformer.and a connection from said input circuit to a point on said path havinga potential substantially equal to the average cathode potential. i

6. An electron discharge device having a thermionic cathode and anoutput circuit, a transformer connected to said cathode for supplyingheating current thereto, a path in shunt to the secondary of saidtransformer, and a connection from said output circuit to a point onsaid path having a potential substantially equal to the averagecathodepotential.

thermionic cathode and an input and an output circuit, a transformerconnected to said cathode for supplying heating current thereto, a pathin shunt to. the secondary of said transformer, and a connection fromsaid circuits to a point on said path having a potential substantiallyequal tothe average cathode otential.

8. Asignaling system comprising an electron disc arge device having athermionic cathode, an input circuit and an output circuit a transformerconnected to said cathode circuits ton point on said tentialsubstantially equa to the average for supplying heating current thereto,a path cathode potential.

in shunt to the second former, said path bein to heating current and onaling currents, and a connection from said ury of said transof highimpedance w impedance to si In witness whereof, I hereunto subscribe myname this 9th day of October,A. D. 1916;

RAYMOND A. HEISINGQ ath having a po-

